Switching amplifiers comprise electronic power switches that have the purpose of controlling loads of various types (e.g. of R, L, C type). Also referring to FIG. 1A, a half-bridge switching amplifier 1 is shown, which is configured to control a RLC load, such as a speaker 4, through a filter 5, such as a low-pass filter (e.g. of the LC type). The power dissipated by the electronic switches 2A, 2B, which in this case are two MOS power transistors (but may also be bipolar transistors or IGBTs) connected in series between a supply voltage reference Vdd and a ground reference GND and controlled by a driver 3 which in turn receives a control signal Vin of pulse width modulated (PWM) type, comprises three contributors.
Particularly, the first contributor to dissipated power is given by the power dissipated due to quiescent current: P(q). This term designates the power dissipated by the device due to the current absorbed by the driver 3 in addition to the control current of the final power transistors 2A and 2B. The second contributor to dissipated power is given by the power dissipated due to conduction: P(c), i.e. the power dissipated by the power transistors 2A, 2B when they are “ON.” Assuming that I(o) is the output current that flows in the power transistors 2A, 2B and V(c) is the voltage at the ends of the load 4, then the instantaneous power P(c) is:P(c)=I(o)×V(c).
If the power transistors 2A, 2B comprise power MOS whose drain-source resistance in the “ON” state is R(on), then the voltage at the ends of the load 4 is:V(c)=I(o)×R(on).A third contributor to dissipated power is given by the power dissipated due to switching: P(s). This term designates the power dissipated by the amplifier 1 during the switching edges of the output wave from zero to Vdd or vice versa. Assuming the load 4 is inductive, the output current I(o) during the switching time t may be deemed to be constant. Also, assuming a linear drain-source voltage ramp Vds, the power dissipated during this time t will be:P(s)=½I(o)×Vdd.If T is the period of the switching frequency fsw, then the average dissipated power due to switching will be:P(s_ave)=2×P(s)×t/T. 
Based on this formula, a person may conclude that, assuming a switching time that tends to zero, the average power dissipated due to switching P(save) will also tend to zero. In practice, due to various reasons, such as the difficulties of controlling and handling excessively high “di/dt” slopes, as well as problems concerning electromagnetic emissions, it may not be possible to reduce the switching time “t” beyond a given limit. The chart of FIG. 1B shows the losses caused by power dissipation due to conduction P(c) (see area 6 of the chart) and by power dissipation due to switching P(s) (see area 7 of the chart) during the period T of the switching frequency fsw.
In order to minimize the power dissipated due to switching, some approaches have developed “resonant,” “quasi resonant” or “soft switching” systems in which, the use of a further resonant LC cell in addition to the one that is generally provided in the output filter, allows the final transistors 2A, 2B of the half bridge to be only turned on when the voltage at their ends is zero or when the output current drops. Generally, these switching systems are more complex than those of a simple bridge switching amplifier as shown in FIG. 1A, as switching systems may require inductors and sometimes additional transformers.